1. Field of the Invention
The present invention relates to an apparatus for recording and replaying information on optical information record medium and an apparatus for replaying information on optical information record medium, and more particularly to an optical information record/replay apparatus capable of recording information into and/or replaying recorded information from an optical information record medium using a focus error signal and a tracking error signal generated from reflected light beams from the optical information record medium.
2. Description of the Related Art
An optical information record/replay apparatus is generally provided with an optical head for recording information into a record medium. The optical bead includes an object lens for focusing a light beam radiated from a light source such as a laser. The object lens is configured movable along the optical axis and information track width direction.
The optical information record/replay apparatus detects the focus error signal and tracking error signal in order to actuate the object lens along the optical axis and the information track width direction in response to the signals. A method and apparatus for detecting the focus error and tracking error signals will be briefly explained below with reference to the drawings.
FIG. 8 is a diagram showing an optical information record/replay apparatus according to the prior art 1. A light source or laser diode 1 radiates a laser light, which enters a deflection beam splitter 2 onto a deflection surface 2a as a P-wave straight polarized light with respect to the polarization surface of the deflection beam splitter 2. Therefore, it mostly passes through the deflection surface 2a and enters a collimator lens 3.
The collimator lens 3 converts an incident laser light into a parallel light. The parallel light becomes a circular polarized light when it passes through a xcex/4 plate 13, and then enters an object lens 4. The object lens 4 collects incident laser lights to form a small spot on an information-bearing surface of an optical disc 5.
Referring also to FIG. 9, light 10 reflected at the information-bearing surface of the optical disc 5 enters the deflection beam splitter 2 through the object lens 4, xcex/4 plate 13 and collimator lens 3. The reflected light is converted into an S-wave straight polarized light at the xcex/4 plate 13. Therefore, it almost reflects at the deflection surface 2a of the deflection beam splitter 2 and enters a complex prism 26.
The complex prism 26 diffract the reflected light into two diffracted light beams as described later. Each diffracted light beam is radiated to a predetermined position of a photodiode substrate including photodiodes or photoreceptor elements (not depicted).
The photodiode receives the reflected light from the optical disc 5 and outputs an optical signal to an arithmetic circuit 14. The arithmetic circuit 14 generates a focus error signal and a tracking error signal from the optical signal and outputs them to a controller circuit 16. A drive circuit 17 supplies a drive current into a magnetic coil in a lens actuator 18. The lens actuator 18 controls the object lens 4 to drive along the focus and tracking directions.
The complex prism 26 and photodiode substrate 8, will be described next using FIGS. 9 and 10A-10C. FIG. 9 is a schematic diagram of the complex prism 26 and photodiode substrate 8. The complex prism 26 and photodiode substrate 8 are positioned at predetermined positions and fixed with a UV setting adhesive and the like.
FIGS. 10A-10C are diagrams obtained from monitoring the reflected light detected at photodiodes 8a and 8b. The six-part split photodiodes 8a and 8b consist of respective photodiodes A-F.
When the small spot on the optical disc 5 is located at the focus position on the information-bearing surface of the optical disc, the reflected light from the optical disc 5 enters a surface 26a of the complex prism 26 so as to converge upon a focus point FP in the diagram.
50% of the incident reflected light 10, for example, enters the photodiode 8a without being reflected from the surface 26b of the complex prism 26. The other 50% on the other hand reflects from the surface 26b of the complex prism 26 at about a right angle and then reflects at a surface 26c and enters the photodiode 8b. 
If a distance relation between the optical disc 5 and the object lens 4 is a desired value, light spots detected at the photodiodes 8a and 8b are monitored as spots having the same diameters as shown in FIG. 10A.
If a distance between the optical disc 5 and the object lens 4 is shorter than the desired value, a spot diameter of the light spot detected at the photodiode 8a becomes larger and a spot diameter of the light spot detected at the photodiode 8b becomes smaller as shown in FIG. 10B.
If a distance between the optical disc 5 and the object lens 4 is longer than the desired value, the spot diameter of the light spot detected at the photodiode 8a becomes smaller and the spot diameter of the light spot detected at the photodiode 8b becomes larger as shown in FIG. 10c. 
When the track advancing direction of the optical disc 5 is as represented by an arrow in FIG. 10, the focus signal can be detected by a spot size method and the track signal can be detected by a push-pull method. Arithmetic equations for use in detection are shown below:
Focus signal=(A+C+E)xe2x88x92(B+D+F)
Track signal=(A+F)xe2x88x92(C+D)
The prior art 2 will be described next using FIGS. 11-13C. FIG. 11 is a diagram showing an optical information record/replay apparatus according to the prior art 2. This optical information record/replay apparatus comprises a grating hologram device 27 and a photodiode substrate 8. FIG. 12 is a diagram showing reflected light in a state of entering the grating hologram device 27. FIGS. 13A-13C are monitor diagrams of the reflected light received at the photodiode 8. Other parts of the optical information record/replay apparatus shown in FIG. 11 are similar to those in the prior art 1.
A hologram grating surface 27a is formed on a surface of the hologram device 27. The hologram grating surface 27a has a grating pattern provided with the following lens power characteristic.
The reflected light 10 from the optical disc 5 is diffracted at the hologram grating surface 27a into three diffracted light beams having a predetermined angle of diffraction. A diffracted light beam of plus first order is characteristically converged upon a near location (close to the hologram surface) relative to a convergence position 12a of a diffracted light beam of zero order that passes through the hologram. A diffracted light beam of minus first order is characteristically converged upon a distant location (apart from the. hologram surface) relative to the convergence position 12a. 
When the reflected light 10 enters the hologram grating surface 27a, it is diffracted at the hologram grating surface 27a into three diffracted light beams including a diffracted light beam of plus first order, a diffracted light beam of zero order and a diffracted light beam minus first order. The diffracted light beams are converged upon the positions 12c, 12a and 12b, respectively In this case, a photodiodes 121, 122, 123 are arranged so as to meet its photoreceptor surface with the position 12a. 
The photodiode substrate comprises a seven-part split photodiode. The seven-part split photodiode includes a three-part split diode 123 consisting of photodiodes A-C, three-part split diode 122 consisting of photodiodes D-F, and photodiode 121 consisting of a photodiode M.
A diameter of the light spot varies in accordance with a distance relation between the optical disc 5 and the object lens 4. If a distance between the optical disc 5 and the object lens 4 is a desired value, a spot diameter of the light spot detected at the photodiode 123 becomes the same as a spot diameter of the light spot detected at the photodiode 122 as shown in FIG. 13B. If a distance between the optical disc 5 and the object lens 4 is shorter than a desired value, the spot diameter of the light spot detected at the photodiode 123 becomes larger and the spot diameter of the light spot detected at the photodiode 122 becomes smaller as shown in FIG. 13A.
If the distance between the optical disc 5 and the object lens 4 is longer than the desired value, the spot diameter of the light spot detected at the photodiode 123 becomes smaller and the spot diameter of the light spot detected at the photodiode 122 becomes larger as shown in FIG. 13C.
When the track advancing direction of the optical disc 5 is as represented by an arrow in FIG. 13, the focus signal can be detected by a spot size method and the tracking error signal can be detected by a push-pull method with the following arithmetic equations:
Focus signal=(A+C+E)xe2x88x92(B+D+F)
Track signal=(A+F)xe2x88x92(C+D)
The above conventional technologies, however, have several disadvantages. The optical information record/replay apparatus in the prior art detects the tracking error signal by the push-pull method. The tracking error signal, however, cannot be detected from a replay-only optical disc such as a DVD-ROM but by a detecting method named DPD (Differential Phase Detection) method. It is because a DVD-RAM which is the objective recording medium of the prior art has a groove for the tracking using a push-pull signal, whereas a DVD-ROM has pits for the tracking using a differential phase detection signal (DPD signal). Therefore, the conventional optical information record/replay apparatus cannot replay information recorded in DVD-ROMs.
In addition, the optical information record/replay apparatus in the prior art detects the focus error signal and tracking error signal from the same photodiodes. Therefore, the split lines for the photodiodes A, B and C (or D, E and F) are required to set parallel to the track advancing direction. As a result, crosstalk effecting from the tracking error signal to the focus error signal causes a large disadvantage.
The spot size method, which is the method of detecting the focus signal, generally has a low sensitivity for detecting focus errors and is difficult, to control the operation of the optical head with a high precise resolution.
The optical information record/replay apparatus shown in the prior art 1 includes the complex prism for use in the optical head. The complex prism is expensive. Therefore, it is difficult to lower the cost of the optical information record/replay apparatus having the optical head with the complex prism.
In order to overcome the above disadvantages, the present invention has been made and accordingly, has an object to provide an optical information record/replay apparatus capable of replaying any optical information record media regardless of types and inexpensively performing a high precise control with less crosstalk. The present invention has another object to provide an optical information replay apparatus capable of replaying any optical information record media regardless of types and inexpensively performing a high precise control with less crosstalk.
According to a first aspect of the present invention, there is provided an apparatus for recording and replaying information on optical information record medium, comprising: a light source for radiating a light beam to an information-bearing layer of the optical information record medium; a hologram device for splitting reflected light from the optical information record medium, the hologram device comprising a central region formed at the central area thereof and a hologram grating surface region arranged at the outer periphery of the central region; a photorecentor device for receiving split light beams from the hologram device, the photoreceptor device comprising a first multiple-part split photoreceptor element for receiving light beams from the central region and two second multiple-part split photoreceptor elements for receiving light beams from the hologram grating surface region, means for generating a tracking error signal from signals from-the first multiple-part split photoreceptor element; means for generating a focus error signal from signals from the two second multiple-part split photoreceptor elements; and means for performing a tracking control and a focus control based on the tracking error signal and the focus error signal, respectively, to record or replay information on the optical information record medium.
According to a second aspect of the present invention, there is provided an apparatus for replaying information on optical information record medium, comprising: a light source for radiating a light beam to an information-bearing layer of the optical information record medium; a hologram device for splitting reflected light from the optical information record medium, the hologram device comprising a central region formed at the central area thereof and a hologram grating surface region arranged at the outer periphery of the central region; a photoreceptor device for receiving split light beams from the hologram device, the photoreceptor device comprising a first multiple-part split photoreceptor element for receiving light beams from the central region and two second multiple-part split photoreceptor elements for receiving light beams from the hologram grating surface region, means for generating a tracking error signal from signals from the first multiple-part split photoreceptor element; means for generating a focus error signal from signals from the two second multiple-part split photoreceptor elements; and means for performing a tracking control and a focus control based on the tracking error signal and the focus error signal, respectively, to replay information on the optical information record medium.
According to a third aspect of the present invention, there is provided an optical pickup, comprising: a light source for radiating a light beam to an information-bearing layer of the optical information record medium; a hologram device for splitting reflected light from the optical information record medium, the hologram device comprising a central region formed at the central area thereof and a hologram grating surface region arranged at the outer periphery of the central region; a photoreceptor device for receiving split light beams from the hologram device, the photoreceptor device comprising a first multiple-part split photoreceptor element for receiving light beams from the central region and two second multiple-part split photoreceptor elements for receiving light beams from the hologram grating surface region.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.